1. Field of the Invention
The present invention relates to an apparatus for detecting a magnitude of torque due to auxiliary devices that are driven by a rotational driving source. In particular, the present invention relates to a apparatus for detecting torque due to auxiliary devices such as an alternator, a compressor and the like that are driven by an internal combustion engine. The present invention also relates to a method for accurately detecting the magnitude of torque due to auxiliary devices.
2. Description of Related Art
A shaft of an internal combustion engine of a vehicle drives various auxiliary devices. A compressor of an air conditioner, an oil pump of an automatic transmission, an oil pump of a power steering device, an alternator, a fan and the like are examples of such auxiliary devices. Meanwhile, to lower the idle engine speed of the internal combustion engine, it will be necessary to accurately determine the load torque applied to the internal combustion engine by such auxiliary devices. Moreover, with more accurate detection of such load torque, the control of the automatic transmission becomes more precise and the operation of the transmission will be smoother. In addition, locking in of the air conditioner compressor can be promptly responded to when such locking is detected. Furthermore, the power steering device can be controlled to detect and issue a warning when a driver performs excessive steering operations.
One common method for detecting the amount of torque in the rotation shaft (driving shaft) detects the amount of torque based on elastic twisting in the rotation shaft that is in accordance with the amount of torque. For this purpose, as disclosed in Japanese Patent Laid Open Publication No. Hei-4-109134, a wire resistance strain gauge is installed in the rotation shaft to detect any slight twisting in the rotation shaft based on the change in the electrical resistance thereof with the amount of torque in the rotation shaft being computed based on such twisting.
In this way, in the aforementioned method, the strain gauge has to be installed on the rotation shaft using an adhesive or the like to measure the amount of twisting or the like. However, the output of the strain gauge varies greatly with respect to how and where it is installed on the rotation shaft and thus, the accuracy of measuring the amount of torque is greatly affected by the configuration of the strain gauge on the rotation shaft.
Moreover, because the rotation shaft to which the strain gauge is installed is rotating, there will be a need for a sliding mechanism such as a slip ring to receive the output signal (electric signal) from the strain gauge. However, such a sliding mechanism may adversely affect the reliability, the durability and the length of the usage lifetime of the strain gauge.